Driven by the rise of GeoWeb 2.0 and the non-stop spread of mobile devices, the practice of Volunteered Geographic Information (VGI) has revolutionized the history of Geographic Information Systems (GIS) by making creation and Web sharing of geospatial data within reach for anyone. This research focuses on the VGI subcategory of citizen science, which concerns citizens' participation into scientific projects involving collection and/or analysis of geospatial information. An architecture entirely based on FOSS (Free and Open Source Software) is developed, which allows to fulfill the typical citizen science requirements, i.e. collection of georeferenced data (including multimedia) from mobile devices; data storage and management through an authentication mechanism; data Web publication through standard GeoWeb protocols; and data Web interaction on multi-dimensional platforms. Different 2D Web applications are built providing an optimized data access for desktop devices and mobile devices. A virtual globe 3D platform is also designed which provides a pool of advanced collaboration-enabling functionalities. The implemented architecture is tested on several civic engagement case studies related to tourism and culture, urban monitoring, urban planning, and water management. A complementary study on the geolocation accuracy of current mobile devices, which represents a crucial factor for the evaluation of VGI quality, is also addressed.